As is well known, a fuel cell is a system for generating electric energy through an electrochemical reaction between oxygen and hydrogen contained in hydrocarbon materials such as methanol, ethanol, or natural gas.
Recently developed polymer electrolyte membrane fuel cells (hereinafter, referred to as PEMFCs) have excellent output characteristics, low operating temperatures, and fast starting and response characteristics. PEMFCs may be used for a wide range of applications including mobile power sources for vehicles, distributed power sources for homes or buildings, and small-sized power sources for electronic apparatuses.
A fuel cell system employing the PEMFC scheme basically includes a stack, a reformer, a fuel tank, and a fuel pump. The stack constitutes an electricity generation set having a plurality of unit cells and the fuel pump supplies fuel from the fuel tank to the reformer. There, the reformer reforms the fuel to generate hydrogen that is supplied to the stack.
The reformer generates hydrogen from the fuel through a catalytic chemical reaction using thermal energy, and includes a heat source section where thermal energy is generated, and a reforming reaction section where thermal energy is absorbed to generate hydrogen from the fuel.
However, in the reformer of a conventional fuel cell system, since the heat source section and the reforming reaction section are typically separated from one another and connected to each other through pipes, there is no direct heat exchange between the sections. Accordingly, such a system generally requires a preheating time for the reforming reaction section, and further, because the heat delivery path is elongated, the thermal efficiency is poor. In addition, since the respective sections are separated, it is difficult to make the system compact.
Furthermore, for a conventional fuel cell system, since the fuel supplied to the reformer generally must be preheated with an additional preheating device, much energy is spent in preheating the fuel, thereby deteriorating the performance and thermal efficiency of the entire system.